The dissociation of oxygen from the hemoglobin molecule, an intregal part of the transport of oxygen, can be described by the oxyhemoglobin dissociation curve. This assessment of the respiratory function of the blood takes on clinical significance in the characterization of congenital hemoglobinopathies, in evaluation of blood oxygen transport capability during respiratory and metabolic acid-base disturbances, and more recently in the evaluation of certain forms of ischemic heart disease. The oxyhemoglobin dissociation curve, together with its characteristic parameter P.sub.50, the partial pressure of oxygen at half-saturation of hemoglobin with oxygen, is known to be affected by changes in temperature, the partial pressure of carbon dioxide, pH, blood organic phosphate concentration and hemoconcentration. Furthermore, the dissociation of oxygen from hemoglobin or whole blood can best be described by a method which measures or controls the majority of these variables, while recording the dissociation process. Presently, there are many methods available for oxygen dissociation curve analysis as, for example, those described by J. D. Torrance and C. Lenfant, in an article entitled "Methods For Determination of O.sub.2 Dissociation Curves, Including Bohr Effect", Respiratory Physiology, Volume 8, pages 127-136 (1970). The most acceptable of these are methods which record the oxyhemoglobin dissociation reaction as a continuous function of blood oxygen tension, and which continuously record pH change in order to assess the Bohr effect on the hemoglobin-oxygen reaction.
The Laver method, described in an article by M. A. Duvelleroy, R. G. Buckles, S. Rosenkaimer, C. Tung and M. B. Laver, entitled "An Oxyhemoglobin Dissociation Analyzer", published in the Journal of Applied Physiology, Volume 28, pages 227-233 (1970), characterizes the oxyhemoglobin dissociation process in this manner. However, this method falls short of perfect assessment of this equilibrium reaction, because it fails to account for changes in the intracellular hydrogen ion concentration or the transcellular hydrogen ion gradient caused by fluctuations in the concentration of the impermeable intracellular anion 2,3-diphosphoglycerate (2,3-DPG). At present there exists no satisfactory prediction formula for the correction of P.sub.50 due to changes in 2,3-DPG concentration. Nevertheless, 2,3-DPG concentration can be measured separately and the P.sub.50 can be interpreted in light of its 2,3-DPG magnitude. Finally, the clinical usefulness of even the Laver apparatus is limited, however, by such factors as cost of apparatus, occasional instability of the gas phase P.sub.02 electrode, time of procedure, method for calculation of P.sub.50, and sample size. The latter of these is a critical limitation in that newborns and young infants do not have a blood volume large enough to justify such a blood sample (approximately 8.0 ml).